1. Technical Field
The present invention relates generally to an actuator and, more particularly, to an actuator for positioning a valve or a damper in a fluid distributing system, such as an air conditioning or heating system where the actuator must return the valve or damper to a "home" position when power is lost (return-to-normal).
2. Discussion
In the HVAC industry, dampers and valves are used to control air and fluid movements within systems. The valves and dampers are generally adjusted automatically by actuators. In some applications it is desired that the actuators move the damper or valve to a predetermined position upon the loss of power. One method of accomplishing this "return-to-normal" feature is to include a spring within the actuator that urges the damping or valving element into the predetermined or normal position upon power loss. In such spring returning actuators it is common that the spring is wound when the valve or damper is displaced from its normal position so that when power is lost the spring can unwind and move the actuator output and thereby the damping or valving mechanism into the appropriate position. U.S. Pat. No. 4,741,508 issued May 3, 1988 to Fukamachi entitled "Actuator For Valve" is an example of this type of actuator.
Due to the various applications for dampers and valves within the HVAC industry, certain applications require movement of the valving element in one direction, e.g., toward a closed position, upon the loss of power whereas in other applications the element must be moved in the opposite direction when power is lost, e.g., to a fully open position. Thus, it is desirable that actuators be capable of being set to move the valving or damping element upon loss of power In either of the two directions. The prior art has not adequately addressed this need. Rather, prior art actuators must either be reversed in orientation relative to the valve or damper or the spring element in the actuator must be reversed in orientation to provide operation in the reverse direction. The reversing of the actuator relative to the valve or damper can make accessing the electronic components of the actuator difficult and the reversal of the spring element within the actuator causes unnecessary manual intervention.
In order to insure proper operation of the actuator and damper/valve, it is also important to maintain the spring in a partly wound condition both during normal actuator operation and after the spring has moved the closure element to its home position. The minimum amount of winding is dictated by the force necessary to maintain the closure element in its "home" position during power loss. However, the present invention recognizes that while a stop arrangement could be provided on the spring input or output to limit unwinding, such an arrangement would undesirably limit the travel of the spring and/or the input/output element to less than one reciprocal movement or revolution. To achieve optimum operation of a spring biased return to normal actuator, it is desirable to wind the spring several reciprocations/revolutions between the minimum and maximum winding positions.